What Are the Selection Factors of Pneumatic Actuators?

 

According to their energy form, actuators are divided into three categories: pneumatic actuators, electric actuators and hydraulic actuators. They have their own characteristics and are suitable for different occasions. Pneumatic actuators are a category of actuators. Pneumatic actuators can also be divided into single acting pneumatic actuator and double acting pneumatic actuator.

 

Selection Factors of Pneumatic Actuators

 

Before installing the electric and pneumatic actuator to the valve, the following factors must be considered.

 

1. The number of turns of the output shaft. This is related to the nominal diameter of the valve, the pitch of the stem, and the number of thread heads. It should be calculated as M=H/ZS (M is the total number of turns that the electric device should meet, H is the valve opening height, and S is the stem drive thread Pitch, Z is the number of stem threads).

 

2. Special requirements. This must be able to limit torque or axial force. When the specifications of the electric device are determined, the control torque is also determined.

 

The opening and closing speed of the output speed valve. If it is too fast, water hammer will easily occur. Therefore, the appropriate opening and closing speed should be selected according to different conditions of use.

 

3. Operating thrust. When choosing air powered actuator, we must also consider its operating thrust. There are two main structures of the pneumatic valve device. One is without a thrust plate and directly outputs torque, and the other is equipped with a thrust plate. The output torque is converted into output thrust through the stem nut in the thrust plate.

 

4. Operating torque. It is the most important parameter to choose the valve electric device. The output torque of pneumatic air actuator should be 1.2-1.5 times the maximum torque of valve operation.

 

Generally speaking, we believe that the torque required to operate the valve comes from the friction between the metal parts of the valve (such as the ball core, the valve disc) and the seal (valve seat). According to the valve application occasions, operating temperature, operating frequency, pipeline and pressure difference, flowing medium (lubrication, drying, mud) and many other factors all affect the operating torque.

 

The valve mainly include pneumatic ball valve, air actuated butterfly valve, plug valve and pneumatic angle seat valve.

 

The operating torque is usually not affected by the pressure of the fluid but is determined by the friction between the valve seat and the plug during opening and closing. The torque is maximum when the valve is closed. Due to the influence of pressure, a high torque is always maintained during the rest of the operation.

 

5. The stem diameter is to the multi-turn type rising stem valve. If the maximum stem diameter allowed by the electric device cannot pass through the stem of the equipped valve, it cannot be assembled into an electric valve. Therefore, the inner diameter of the hollow output shaft of the electric device must be larger than the outer diameter of the stem of the rising stem valve. For part-turn valves and dark-stem valves in multi-turn valves, although there is no need to consider the passage of the stem diameter, the stem diameter and the size of the keyway should be fully considered when selecting and matching, so that it can work normally after assembly.